The invention relates to apparatus and method for vapor distilling larger quantities of higher purity polonium and condensing same into a container for a nuclear fuel.
Polonium-210 is normally obtained by the irradiation of bismuth with neutrons in a nuclear reactor according to the following equations: EQU .sup.209 Bi + n .fwdarw..sup.210 Bi + gamma (1) ##EQU1## In this process, bismuth may be cast into about 10 kilogram slugs and an aluminum jacket of about 6 millimeter wall thickness may be placed around each slug prior to its being placed into the reactor. Appropriate irradiation cycle for the slugs varies depending upon the neutron flux; from 60 to 300 curies (Ci) of polonium may be produced per kilogram of bismuth.
There are various processes for separating the polonium from the bismuth. One process is such as described in U.S. Pat. No. 3,271,320 entitled "Polonium Recovery". That patent sought to overcome the therein stated problem of vacuum distillation as to ability to vacuum distill on a large scale, and the shielding due to radioactivity of vapors formed. Another method for separating polonium from bismuth involved removing the aluminum from the irradiated slug by dissolution in hydrochloric acid and dissolving the bismuth in aqua regia. Excess nitric acid in this latter reaction was destroyed with formic acid at from about 85.degree. to about 90.degree.C. Polonium was thereafter separated from the bismuth and purified using a series of deposition and redissolution steps concluding with an electrolysis step wherein the polonium could be cathodically deposited on platinum gauze under controlled electrolytic conditions. This other method likewise was somewhat limited to the amount of polonium that could be processed in a given time. Further, the polonium which was deposited on the platinum gauze generally required further purification for use as a radioisotopic fuel.